1. Field of the Invention
The present invention relates to position determination of mobile devices.
2. Description of the Related Art
With ever-increasing prevalence of handy, mobile devices (e.g. PDAs) in connection with exhaustive availability of digital transmission technologies (e.g. WLAN, etc., UMTS, GPRS), the market for applications providing the user with location-relevant information in every situation is growing. For this reason, the importance of efficient localization of mobile devices for modern, user-friendly applications is growing.
In the area within buildings (indoor area), the development of suitable localization methods is a challenge, because walls and fixtures may render the employment of common positioning technologies significantly difficult or impossible. But especially within buildings or in the combined indoor and outdoor area, manifold localization-dependent applications arise, such as guidance systems for finding rooms, things and employees, patient emergency systems in the medical area, or applications in the field of workfloor management.
In order to be able to perform this assistance in sensible manner, it is inevitable for a participant to be able to query his or her position in the building at any time (or at any place of the building, which means complete coverage).
The known methods for position determination, for example, are GPS, triangulation via runtime measurements, or also radio cell recognition through base station identification. In these concepts, however, their great complexity, which is connected to high costs, as well as maybe high inaccuracy, is disadvantageous.
WO 02/054813 A1 discloses a method for estimating a position of a receiver in a wireless communication environment having several channels. Each channel has at least one signal parameter that varies depending on the position, with this variation being different for each channel. A set of calibration data is determined for each calibration point, each set including the position and at least one measured signal parameter for each of the channels. The calibration data serve as a basis for a statistical model of the signal parameters depending on a position of the receiver. Furthermore, a set of observed signal parameters, which includes at least one signal parameter for each of the plurality of channels, is determined. On the basis of the statistical model and the set of the observed signal parameters, the position of the receiver is approximated. Since this method starts out from the assumption that a different signal parameter, which is different from all other signal parameters for this channel and at a certain position, can be associated with each of the channels, this method can be employed exclusively for such a scenario. A further disadvantage in the concept disclosed in the above reference, is that the statistical model is acquired on the basis of a probability distribution, which is connected with high computation complexity as well as residual insecurity with respect to the position of the receiver.
EP 1022578 A2 concerns a device using radio signal strength to estimate the momentary position of a mobile body relative to a map. The device periodically receives a set of measured values of the radio field strength of respective radio signals from a plurality of base stations from the mobile body, stores these sets and applies averaging methods to the entire sequence of sets of measured radio signal strength values so as to obtain a corresponding sequence of sets of smoothed radio signal strength values. Based on previously measured values of the radio signal strength, which have been obtained previously for each of a plurality of predetermined points, such as road intersections, the device is effective, with respect to the sequence of sets of smoothed radio signal strength values, to estimate those of the predetermined points that have been crossed by the mobile body one after the other until the momentary point in time, in order to thereby estimate the momentary position of the mobile body.
From WO 98/15149, a method for localizing a mobile station is known, in which information received and measured by a mobile station is transmitted to a network management system. The information is compared with the field strength information in a field strength matrix, wherein the location of the mobile station is estimated as coordinates of the field strength matrix relative to the base station of the serving cell and the base station of a neighboring cell in such manner that the information received and measured by the mobile station corresponds to the field strength information in the field strength matrix in as accurate a manner as possible.